Integrin a3b1 is an extracellular matrix receptor that is expressed in many malignant tumors and has been shown to regulate cellular phenotypes associated with epithelial-to-mesenchymal transition (EMT), such as cell proliferation, survival, and invasion. Expression of matrix metalloproteinase MMP-9 is also linked to malignant tumor growth, where it promotes tumor angiogenesis and cell invasion. a3b1 induces MMP-9 in immortalized keratinocytes (MK cells) through post-transcriptional mRNA stability, and this regulation is acquired during cellular immortalization. However, the mechanisms and signaling pathways whereby a3b1 regulates MMP-9 mRNA stability and their roles in tumor growth and progression are unknown. The goal of the proposed research is to answer these questions by exploiting a panel of a3b1-expressing (i.e. a3 wild type) and a3b1- deficient (i.e., a3-null) MK variants that collectively represent different EMT stages: (1) non-immortalized keratinocytes are isolated from neonatal epidermis; (2) immortalized MK cells harbor a p53-null mutation; (2) transformed MK cells additionally express oncogenic RasV12. Loss of p53 and oncogenic Ras activation are common mutations in squamous cell and other carcinomas. Preliminary data from this model indicate that a3b1 and MMP-9 are required for in vivo tumor growth of MK cells, and identify candidate signaling pathways and mechanisms whereby a3b1 may control MMP-9 mRNA stability. The proposed studies will test the hypotheses that MMP-9 mRNA expression is controlled by specific a3b1-mediated signaling pathways that control mRNA stability, and that these mechanisms control tumor growth in vivo. A combination of molecular, genetic, and biochemical approaches will be used to identify mRNA regulatory elements that control a3b1- dependent mRNA stability, and to elucidate specific signaling pathways or integrin functions that are involved in a3b1-mediated MMP-9 mRNA stability. An in vivo tumorigenesis model will be used to investigate the role of a3b1-dependent regulation of MMP-9 for tumor growth. Finally, the human relevance of these observations will be investigated by testing for a3b1-dependent regulation of MMP-9 in several human carcinoma lines, and by assessing expression of a3b1 and MMP-9 in human tumor specimens.